Application Cases

Experiment Name: Research on Defect Detection Based on Stress Waveguide Technology

Research Focus: Non-Destructive Testing, Defect Localization

Experimental Objective:
To conduct experimental research on pipeline defect detection using the piezoelectric sensing method, and to explore the feasibility of this method for detecting pipeline defects.

Testing Equipment:
ATA-8202 RF power amplifier, signal generator, test specimen, oscilloscope

Experimental Procedure:
A PZT ring serving as the actuator generates stress waves, which propagate through the structure and are received by PZT piezoelectric patches acting as sensors. When the structure contains defects, the energy of the propagating stress waves diminishes. The stress wave signals received by the PZT piezoelectric patches are weaker compared to those in a defect-free state. The severity of the defects corresponds to a reduction in the received stress wave energy, enabling defect detection in the structure.

Figure: Schematic Diagram of the Experiment

The experimental setup consists of a signal generator, an oscilloscope, an ATA-8202 power amplifier, and various test specimens. In this experiment, piezoelectric patches that deform along their length and piezoelectric rings that deform along their thickness are used. Sixteen piezoelectric patches are connected in parallel and attached to the pipeline specimen, while a piezoelectric ring is fitted over one end of the pipeline. The experiments reveal an effective frequency band for guided wave detection, with the optimal frequency range for defect detection being 25 kHz to 100 kHz. A sinusoidal excitation signal with an amplitude of 10 V is applied to the piezoelectric ceramic sensor acting as the actuator. However, generating ultrasonic guided waves via piezoelectric materials requires a voltage signal of approximately 200 Vpp. Therefore, a power amplifier is used to drive the piezoelectric ring to produce stress waves, which propagate through the pipeline specimen and are sensed by the piezoelectric sensors at the receiving end. Due to the piezoelectric effect, the collected stress wave signals are converted into voltage signals. The voltage signals from the receiving piezoelectric sensors are then captured by the oscilloscope. By comparing the differences in the signals before and after, defect information in the pipeline can be obtained.

Figure: Experimental Equipment Setup

Experimental Results:
The stress wave signals collected by the receiving piezoelectric sensors are shown in Figures 3, 4, 5, and 6 below.

Figure 3: Test Signals of Incident Waves at Different Frequencies in an Intact Pipeline

Figure 4: Test Results of Pipeline Defect Detection Under Specific Frequencies with Different Cycle Signals

Figure 5: Failure to Identify Defects Due to Inappropriate Frequency Selection

From the figures above, it is evident that the cycle count and frequency of the excitation signal play a decisive role in the test results. With a 5-cycle excitation signal, the bending mode in the incident signal is prominent. The selection of the cycle count should take into account the length of the pipeline being tested. To avoid overlap between the echo signal and the incident signal, larger cycle signals are more suitable for defect detection. When an inappropriate frequency is selected, defect information may be missed. Additionally, high-frequency signals can lead to the emergence of higher-order bending modes. Therefore, in defect detection based on guided waves, apart from determining the approximate frequency range using dispersion curves, the test frequency should be adjusted in actual measurements to achieve optimal results. After determining the specific frequency and cycle count, the test results are as shown in Figure 6, where pipeline defects are clearly detected.

Figure 6: Final Experimental Results

Reasons for Selecting This Power Amplifier:
High voltage accuracy, wide bandwidth, excellent output waveform, and user-friendly operation.

Figure: Specifications of the ATA-8000 Series RF Power Amplifier